Michael J. Chapman

Endosymbioses: cyclical and permanent in evolution

the cohabitation of organisms of different species, whereas endosymbiosis is a topological condition: one organism lives inside another. Understanding endosymbioses, which may be intraor extracellular, is of extraordinary importance for medical microbiology. Ironically, although most of the disease conditions described in Trends Microbiol. are, in fact, variations on the general theme of cyclical endosymbioses, very few medical microbiologists are familiar with the insightful, burgeoning literature that demonstrates these widespread associations1–3. Symbioses usually, if not always, have environmentally contingent outcomes (Box 1). Symbiosis, which is not an evolutionary process per se, refers to physiological, temporal or topological associations with environmentally determined fates. Symbiogenesis, however, is a type of evolutionary innovation that describes the appearance of new tissues, new organs, physiologies or other new features resulting from protracted symbiotic association4,5. Unfortunately, evolutionary analysis, especially of endosymbiogeneses, is seldom applied to the study of infectious disease, and such relationships are obscured by dismissive, oversimplified and often meaningless labels; for example, ‘parasite’, ‘pathogen’ and ‘disease agent’. Note that the symbiotic relationships in Box 1 may use any of these labels. These obfuscating and overused terms tend to be applied as though they are explanatory. Here, we aim to point the reader towards pertinent literature rather than make amends. The cells of all large organisms, such as vertebrates, are the products of symbiogenesis. At the beginning of any symbiotic association, the free-living organism is restricted by a membrane of its own making; it contains DNA as genes, proteins, RNA and all other accoutrements characteristic of the free-living condition. The former free-living entities (purple nonsulfur bacteria and cyanobacteria) that became organelles (mitochondria and plastids) must therefore have started with features characteristic of all free-living organisms. Such permanent acquisition of symbionts contrasts sharply with cyclical symbiotic associations, in which each new generation must reacquire symbionts. For mitochondria and plastids, the story has an end: organelles permanently lose their ability to live outside cells, whose dependence on organellar functions becomes equally absolute (Table 1). L. Margulis* and M.J. Chapman are in the Dept of Geosciences, University of Massachusetts, Amherst, MA 01003-5820, USA. *tel: 11 413 545 3244, fax: 11 413 545 1200 Endosymbioses: cyclical and permanent in evolution

Centrioles and kinetosomes: form, function, and evolution.

We review the literature on centrioles, kinetosomes, and other microtubule organizing centers (MTOCs) in animal, plant, and protist cells in the context of the Henneguy-Lenhossék theory of 1899. This 100-year-old cytological theory, valid today, defines centrioles and kinetosomes as identical, homologous but developmentally distinguishable structures. Centrioles (paired constituents of mitotic centrosomes in animal cells) become kinetosomes (ciliary basal bodies) when their 9(2)+2 microtubular axonemes grow outward. During mitosis in Chlamydomonas, the kinetosomes are segregated at the poles of the mitotic spindle. Mitotic centrioles function as organelles of motility in many protists, though nowhere is this centriole-kinetosome relation more clearly seen than in the karyomastigont structure (kinetosome-nucleus-Golgi complex organellar system) of the trichomonads and other amitochondriate parabasalids. Constituent sequences of mitotic spindle-centriole-kinetosome proteins (γ-tubulin, pericentrin, and the cyclin-dependent kinases Cdc2 and Cdc3, members of the centrin family) are conserved across taxa, occurring in animal and protist centrioles, plant MTOCs, and fungal spindle pole bodies. We review ultrastructural and molecular data on these and other important MTOC proteins, and present a model whereby the cytological arrangement of centrioles (i.e., orthogonal pairs as in centrosomes) may have originated. We compare and contrast endogenous and exogenous (bacterial symbiont integration) models for the evolution of centriole-kinetosomes (c-ks), with illustrative examples from Kingdom Protoctista.

Spirochete round bodies: syphilis, Lyme disease & AIDS: resurgence of "the great imitator"?

We advocate investigation of spirochete cyclical symbioses (e.g.,Borrelia sp.,Leptospira sp., Treponema sp.) given the newly established verification of a developmental history in these gram-negative motile helical eubacteria, both in pure culture and in mammals. Symbiotic spirochetes can be compared to free-living relatives for their levels of integration (behavioral, metabolic, gene product or genetic levels), Detailed research that correlates life histories of symbiotic spirochetes to changes in the immune system of associated vertebrates is sorely needed. Genome analyses show that in necrotrophic symbioses (Borrelia andTreponema sp.) of humans and other primates, integration of the bionts occurs at the gene product and genetic level. Spirochete round bodies (also called cysts, L-forms and sphaeroplasts) can be induced by many types of unfavorable conditions (e.g., threats of starvation, desiccation, oxidation, penicillin and other antibiotics). Reversion to familiar helical, motile active swimmers by placement of pure cultures into favorable environments in some cases can be controlled. These observations are supported by a European literature, especially Russian, apparently unknown to American medicine and medical research.

Semes for Analysis of Evolution: de Duve's Peroxisomes and Meyer's Hydrogenases in the Sulphurous Proterozoic eon

Semes for analysis of evolution: de Duves peroxisomes and Meyers hydrogenases in the sulphurous Proterozoic eon

Effect of genome-plastome interaction on meiosis and pollen development in Oenothera species and hybrids

Abstract Oenothera villaricae Dietrich and Oe. picensis Dietrich, complete translocation heterozygotes, are fully interfertile, giving rise to six discrete classes of true-breeding hybrids from a reciprocal cross. Associated with each parent and hybrid is a characteristic abortive non-staining pollen fraction easily distinguished from fully developed pollen under the light microscope. Pollen abortion has been associated with translocation rings in other angiosperm species, and may characterize such systems. The abortive pollen fraction is significantly different between reciprocal Oenothera hybrids, however (P<0.001), indicative of partial cytoplasmic control. Pollen abortion is most severe in the F1 hybrid generation, and ameliorates with successive generations of hybrid self-fertilization. Three-way analysis of variance shows significant effects on pollen stainability (a measure of the non-abortive fraction) for nucleus, cytoplasm and selfed hybrid generation, individually or in combinations. This result suggests a combined nucleocytoplasmic basis for the pollen abortion. Correlated with the observation of increased pollen abortion in Oenothera hybrids are meiotic findings of broken chromosome rings (chains, univalents), asymmetric anaphase chromosome distributions and trinucleate tetrads. To test the hypothesis that such anomalous meiotic events play a role in the mechanism of pollen abortion, meiotic disjunction frequency was determined for each parent, F1 and F9 selfed hybrid accessions. Three-way analysis of variance shows levels of significance comparable to those noted for pollen stainability (P<0.001) for effects of nucleus, cytoplasm and selfed hybrid generation on disjunction frequency. A high degree of correlation (r2=0.984) is noted between disjunction frequency and pollen stainability. We conclude that the abortive pollen grains are indeed the products of nondisjunctional meiotic events, which themselves are consequences of hybrid nucleocytoplasmic incompatibility.

KINGDOM PROKARYOTAE (Bacteria, Monera, Prokarya)

Kingdom Bacteria comprises all organisms with prokaryotic cell structure: they have small ribosomes surrounding their nucleoids, but all lack membrane-bounded nuclei. Sexuality produces genetic recombinants temporally and spatially independent of reproduction. Branched filaments with terminally and/or cyclically differentiated cells (for example, heterocysts, endospores) are among the most structurally complex. All major modes of metabolism are represented in the group in the chapter. Maximum metabolic diversity and lithospheric (geologic) and atmospheric interaction are relative to eukaryotes. The fossil record of bacterial communities extends from the lower Archean eon to the present. A comparison of gene sequence in ribosomal RNA (rRNA) molecules is useful for the identification and distinction of modern lineages. This chapter presents all prokaryotae in the single kingdom Bacteria organized into 2 subkingdoms—Archaebacteria and Eubacteria—and 14 Phyla. The taxa of the prokaryotes, consistent with Bergeys Manual , reflect not only molecular sequence data but also physiology, biochemistry, ultrastructure and habit, ecological niche, and symbiotic association.

Confocal Optical Sectioning for Meiotic Analysis in Oenothera Species and Hybrids

We present a photomicrographic technique for analysis of meiosis in Oenothera species and hybrids. In many species, the 14 isomorphic, 1-2 microns chromosomes are organized into a permanent translocation ring. Interspecific hybrid meiotic analysis is complicated by variations in homology between chromosome sets (Renner complexes) of allospecific origin. Though most wild species from complete rings of 14 at meiosis, hybrids often form combinations of smaller rings and bivalents. There is evidence that asynapsis (chain and univalents) also frequently occurs in hybrids. The greater complexity of hybrid meiotic organization can hinder resolution of individual chromosomes in such chains and small rings and encumber photomicrography of all chromosomes in a cell. Confocal laser scanning microscopy (CLSM) offers a new cytogenetic approach in ring-forming Oenothera species and hybrids. Fortunately, crystal violet, the stain classically used with this difficult material, fluoresces at an excitation wavelength of 488 nm and may thus be employed with the CLSM. Serial projection of image maxima from Z-axis confocal optical sections enables the investigator to count chromosomes and establish pairing relationships, regardless of chromosomal distribution.

The karyomastigont as an evolutionary seme.

The problem of eukaryogenesis—the evolutionary mechanism whereby eukaryotic cells evolved from prokaryotes—remains one of the great unsolved mysteries of cell biology, possibly due to the reductionist tendency of most scientists to work only within their subdisciplines. Communication between biologists who conduct research on the nucleus and those working on the cytoskeleton or endomembrane system are sometimes wanting, and yet, all of these quintessentially eukaryotic elements of the cell are interdependent, and are physically associated in many protists as the karyomastigont organellar system: nucleus, one or more basal bodies and flagella, nuclear connector, and Golgi apparatus. Here we suggest a more holistic view of the karyomastigont as not simply an organellar system, but an evolutionary seme, the archaic state of the eukaryotic cell. We also present a scheme whereby the karyomastigont may have dissociated, giving rise in more derived cells to one or more free nuclei and discrete flagellar apparati (akaryomastigonts).

Chapter Five - KINGDOM PLANTAE

Publisher Summary Members of the plant kingdom develop from embryos—multicellular structures enclosed in maternal tissue. Because all plants form embryos, they are all multicellular. Furthermore, because embryos are the products of the sexual fusion of cells, all plants potentially have a sexual stage in their life cycle. In the sexual stage, the male cell (sperm nucleus, haploid) fertilizes the female egg (embryo sac nucleus, haploid). Many plants grow and reproduce in ways that bypass the two-parent sexual fusion—all must have evolved from ancestors that formed embryos by sexual cell fusion. Plants are adapted primarily for life on land, although many dwell in water during part of their life history. Plants are the organisms most responsible on land and in shallow marine environments for transforming solar energy, water, and carbon dioxide into photosynthate: food, fiber, coal, oil, wood, and other forms of stored energy. Some half million species of plants have been described. Two great groups—the nonvascular plants (informally called bryophytes, also called Bryata, Pl-1 through Pl-3) and the vascular plants (Tracheata, Pl-4 through Pl-12)—constitute the plant kingdom. The chapter refers to the 12 “phyla” of the plant kingdom, but “division” is the term used by some botanists instead of “phylum.”